Very thin steel sheet and method of producing same

ABSTRACT

A full-hard killed steel sheet of a maximum gauge of 0.0140 inch having a corrosion-resistant coating thereon, the steel having a minimum yield strength of 100,000 psi. and sufficient formability to be fabricated into can ends and double seamed onto can bodies. The steel is given a single cold reduction of 65 to 95 percent and coated in its full-hard condition.

United States Patent 1 Mayer et al.

[ 1 Nov. 13, 1973 VERY THIN STEEL SHEET AND METHOD OF PRODUCING SAME OTHER PUBLICATIONS Richards, P. N.; Short-time Annealing Characteristics of Capped, Rimmed and Semi-Killed Wide Strip; Production of Wide Steel Strip, Pages 118-127; Iron and Steel Institute Special Report 67, (1963).

Richards, P. N.; The Effects of Heating Rates and Subrecrystallization Heat Treatments on Aluminum Killed Deep Drawing Steel; Recent Developments in Annealing; Special Report 79 of the Iron and Steel Institute London; pp. 23-33 Roberts, W. J. 5.; Metallurgical Principles and Practice in the Manufacture of Cold-Reduced Tinplate; Production of Wide Steel Strip; Special Report No. 67 of The Iron and Steel Institute London; pp. 95-102 (1960) Primary Examiner-W. W. Stallard Att0rneyJ oseph J. OKeefe [57] ABSTRACT A full-hard killed steel sheet of a maximum gauge of 0.0140 inch having a corrosion-resistant coating thereon, the steel having a minimum yield strength of 100,000 psi. and sufficient formability to be fabricated into can ends and double seamed onto can bodies. The steel is given a single cold reduction of 65 to 95 percent and coated in its full-hard condition.

11 Claims, 3 Drawing Figures 35 E. .Ei... .30 l

PER CENT MANGANESE PER CENT SULFUR PATENTEnnov 13 I973 SHEET 2 [IF 2 5 4 O 4 5 I 3 O "A X 0 a X m X n o O. 5 2 v. X I m f i I 0 o I Q A 5 O I m O. 5 0 Z fiv- O O 5 O 5 O 5 o 5 o 5 o 5 o PER CENT SULFUR INVENTORS Edward H. Mayer Frederick E. Schun/r Hilton N. Ra/m VERY THIN STEEL SHEET AND METHOD OF PRODUCING SAME BACKGROUND OF THE INVENTION This invention relates to very thin sheet steel having very high yield strength and sufficient formability to be fabricated into can ends, and more particularly to a full-hard killed sheet steel having such properties. This invention further relates to a method for producing such a sheet steel.

In recent years the can companies have switched to thinner gauge steel for manufacturing can ends for beer and carbonated beverages. However, in order to use thinner gauges, e.g. sheet steel having a maximum thickness of 0.0140 inch, the minimum yield strength of the steel had to be increased above that for the prior, thicker gauges in order to withstand the internal pressures in the can which are built up during pasteurization or storage. In addition, the steel had to have sufficient formability so that it could be readily fabricated into can ends and double seamed onto can bodies. Current specifications call for steel with 100,000 psi. minimum yield strength in gauges even thinner than 0.0140 inch, viz. about 0.0090 to 0.01l5 inch.

In order to economically produce steel of such thin gauges having such a high yield strength as well as the desired formability, it was previously believed necessary to use a low carbon capped or rimmed steel to which strengthening elements such as nitrogen or phosphorus had been added, and to process the steel in such a manner that additional strength was imparted thereto. The steel was processed in the standard manner through the hot rolling step. Following hot rolling, the steel was cold reduced 60 percent or more to within about 30 percent of final gauge. The steel was not cold reduced directly to final gauge, as it was found that a capped or rimmed steel in the above-referred-to very thin gauges lacked sufficient formability in the fullhard condition to be satisfactorily fabricated into can ends. By full-hard is meant a steel which has not been heat treated to restore softness and ductility after a cold reduction of 65 percent or more. It was therefore necessary to anneal the cold-reduced steel after reduction to intermediate gauge, and then further cold reduce the steel by an additional 30-35 percent to final gauge. The second reduction imparted the required strength to the steel, while still retaining sufficient formability for the fabrication of can ends and double seaming thereof. This method, which is widely used today, is known as the double-reduced" or duo coldreduction" process.

Steel produced by the double-reduced process for can end stock has a minimum yield strength of 100,000 psi. and a minimum of 3 percent transverse dynamic elongation, this percentage being considered necessary for these steels for consistently satisfactory formability. While the double-reduced process is economical and generally gives satisfactory results during can end fabrication, it has been found that occasional lots yield a high incidence of curl" cracking during forming of the can ends or double seaming of the can end onto the can body. A curl crack is a crack which occurs along the rim of the can end.

It is an object of our invention to provide a very thin full-hard steel sheet having a minimum yield strength of 100,000 psi. and sufficient formability to be fabricated into can ends and double seamed onto can bodies with a low susceptibility to curl cracking. It is a further object to provide a method for producing such a steel sheet in a simplifed manner, which method includes only a single cold reduction and omits any annealing operations.

SUMMARY OF THE INVENTION We have discovered that very thin gauge steel strip having a yield strength of at least 100,000 psi. and sufficient formability to be fabricated into can ends and double seamed onto can bodies in its full-hard condition can be produced by hot rolling to intermediate gauge a killed steel having a composition within a relatively narrow range and containing a certain kind of nonmetallic inclusion, and then cold reducing the steel by to percent directly to final gauge. By directly to final gauge is meant without intermediate annealing.

This sufficient formability is obtained when the nonmetallic inclusions in the steel are present predominantly in the form of small discrete particles well dispersed throughout the ferrite matrix. Such a condition exists in steels which have been killed by vacuum deoxidation, by additions of killing agents such as aluminum, or by combinations of both. Other killing agents, e.g. zirconium, vanadium, boron and titanium, which result in the same general type of nonmetallic inclusions, may be substituted for, or used in combination with, aluminum. However, killing agents such as silicon, which result in large, elongated inclusions in the steel, must not be present in substantial quantities.

Other elements which combine to form large, elongated inclusions, e.g. sulfur, which combines to form large, elongated inclusions, must also be limited in quantity.

We have also discovered that when the carbon in the steel is equal to or less than 0.08 wt. percent and the sulfur is greater than 0.020 wt. percent, the manganese in said steel must be equal to or less than 0.40 wt. percent in order to prevent excessive curl cracks. This is quite surprising in several respects. First of all, it is surprising, as well as contrary to general metallurgical practice, that the manganese must be limited or decreased if the sulfur is raised above a certain level. Secondly, it is surprising that this relationship between manganese and sulfur ceases to exist if the carbon in the steel is increased above a certain level.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are photomicrographs showing the size, shape and the distribution of the nonmetallic inclusions in prior art steelsand in the steels of the invention, respectively. 7

FIG. 3 is a graph showing the effect of variations in manganese and sulfur on can end fabrication when the carbon content of the steel is equal to or less than 0.08 wt. percent.

DESCRIPTION OF THE PREFERRED EMBODIMENT Broadly, the invention relates to full-hard steel sheets having a maximum thickness of 0.0140 inch, the steel cles well dispersed throughout the ferrite matrix. In addition, the weight ratio of the manganese to the sulfur must be at least 8:1 to prevent hot shortness, and if the carbon is equal to or less than 0.08 wt. percent and the sulfur is greater than 0.020 wt. percent, the manganese must be equal to or less than 0.40 wt. percent if curl cracks are to be prevented during fabrication of can ends or double seaming of the can end onto the can body. The sulfur must be limited to 0.040 wt. percent max. to insure a good surface on the strip, while nitrogen must be limited to 0.008 wt. percent max. to prevent excessive cracking during can end fabrication. By balance iron we do not wish to exclude residual impurities and incidental elements which may be present in amounts which do not substantially detract from the novel properties of the sheet steel. By killed is meant that the oxygen content of the steel is reduced to such a level that substantially no reaction occurs between carbon and oxygen during solidification of the steel.

While the steels to which the invention is applicable may be killed either by vacuum deoxidation and/or by the addition of one or more members of the group consisting of aluminum, zirconium, vanadium, boron and titanium, said steels preferably are aluminum-killed, and consist essentially of 0.04 to 0.08 wt. percent carbon, 0.25 to 0.40 wt. percent manganese, 0.030 wt. percent maximum sulfur, 0.008 wt. percent max. nitrogen, 0.02 to 0.10 wt. percent aluminum, balance iron.

Steels of the above compositions may be produced by conventional ingot casting or by continuous slab casting practices and hot rolled into strip in the usual manner. For example, a slab of steel may be hot rolled with a finishing temperature of 1,500 to 1700 F., and coiled at 1,000 to 1,400 F. Preferably, the hot rolling is finished at 1,550 F. minimum and the strip is coiled at l,l F. minimum to yield an optimum combination of hot-rolled properties, e.g. a relatively soft and largegrained steel with fine, uniformly distributed carbides.

Following hot rolling, the steel strip is pickled to remove mill scale. The steel strip is then cold reduced by 65 to 95 percent directly to a final gauge of 0.0140 inch max., preferably from 0.0090 to 0.0115 inch, to impart to said steel strip a minimum yield strength of 100,000 psi. and a good surface.

The cold-rolled strip may be directly coated, on either one or both sides thereof, while it is in its full-hard condition. While the coating may be either organic or inorganic, it should be one which can be applied without raising the temperature of the steel above that at which properties of steel in the full-hard condition are substantially altered.

FIG. 1 is a photomicrograph, at 500 magnifications, showing the size, shape, and distribution of the nonmetallic inclusions in a typical prior art steel, viz. a nitrogen-strengthed capped steel. As can be seen, the inclusions are rather large and of the stringer-type.

FIG. 2 is a photomicrograph, at 500 magnifications, showing the nometallic inclusions in steels to which the subject invention is applicable. These inclusions are well dispersed and much smaller than those shown in FIG. 1.

FIG. 3 is a graph showing the effect of variations of manganese and sulfur on can end fabrication. The samples in all cases contained 0.08 wt. percent carbon or less, inasmuch as the relationship shown in FIG. 3 does not hold for higher carbon contents.

All of the samples were actually fabricated into can ends. The x's" on the graph represent samples which cracked when fabricated, while the dots represent samples which were satisfactorily fabricated into can ends.

The dotted line A separates the samples which were satisfactorily fabricated from those which were not, and shows that the manganese must be limited to 0.40 wt. percent max. when the sulfur exceeds 0.20 wt. percent. Also included in FIG. 3 is a solid line 8'' showing the manganese to sulfur ratio of 8:1. In order to prevent hot shortness, all samples must have manganese and sulfur contents which fall above line B.

EXAMPLE 1 As a specific example of the invention, we produced an ingot of aluminum-killed steel of the following analysis:

Wt. Carbon 0.05 5 Manganese 0 .29 Phosphorus 0.004 Sulfur 0.0 l 3 Nitrogen 0.006 Aluminum 0.086

Balance iron The steel was killed by aluminum additions to the mold and ladle.

The ingot was slabbed and then hot rolled into strip 0.076 in. thick. The finishing temperature was l,595 F and the strip was rapidly cooled by water sprays to about 1,100 F. and coiled. The coil of strip, weighing about 11,000 lbs, was allowed to cool slowly in air to room temperature.

The hot-rolled steel strip was then pickled and cold reduced by 87 percent to a final gauge of 0.010 in. The so-prepared strip was then washed and temper rolled to improve its shape, said temper rolling resulting in a 1% percent elongation. The strip was passed directly into an electrolytic tinning line where it was coated with 0.25 lb. of tin per base box. The tin was then fused, the temperature of the steel rising to about 500 F. during the fusion. Samples of the coated strip were tested and found to have a longitudinal yield strength of 103,600 psi. and a transverse dynamic elongation of 4.75 percent. Can ends were readily fabricated therefrom and were double seamed onto can bodies. No curl cracks resulted and the material was satisfactory in every respect.

EXAMPLE 2 A second ingot of aluminum-killed steel was produced, said steel having the following composition:

Wt. Carbon 0.039 Manganese 0.30 Phosphorus 0.004 Sulfur 0.01 2 Nitrogen 0006 Aluminum 0.076

Balance iron The steel was killed by aluminum additions to the mold and ladle.

The ingot was slabbed and then hot rolled into strip 0.076 in. thick. The finishing temperature was 1,570 F., and the strip was rapidly cooled by water sprays to about 1,095 F. and coiled. The coil of strip, weighing about 1 1,000 lbs., was allowed to cool slowly to room temperature.

The hot-rolled steel strip was then pickled and cold reduced by 87 percent to a final gauge of 0.010 in. The so-prepared strip was then washed and temper rolled to improve its shape, said temper rolling resulting in a percent elongation. The strip was passed directly into a chromium plating line where it was coated with 0.36 microinch thick chromium. Samples of the coated strip were tested and found to have a longitudinal yield strength of 1 12,250 psi. and a transverse dynamic elongation of 4.25 percent. Can ends were readily fabricated therefrom and were double seamed onto can bodies. No curl cracks resulted and the material was satisfactory in every respect.

EXAMPLE 3 A heat of aluminum-killed steel was continuously cast, said steel having the following composition:

Wt. Carbon 0.048 Manganese 0.27 Phosphorus 0.006 Sulphur 0.030 Nitrogen 0.003 Aluminum 0.043

Balance iron Two as-cast slabs from this heat were hot rolled into strip 0.076 inch thick using a hot mill practice similar to that described in Example 1. Each coil of strip was then pickled and cold reduced by 87 percent to a final gauge of 0.010 inch. After washing, each coil of strip was temper rolled to improve its shape. One coil was electroplated on an alkaline tinning line. The other coil was chrome plated on a second plating line.

Samples from the two coils were tested in the plated condition. The average yield strength of these samples was about 108,900 psi., and can ends were fabricated therefrom without the occurrence of curl cracks.

While the above examples include the steps of washing and temper rolling the cold-reduced strip, these steps are not essential to the invention, as cold-rolling mills equipped with modern gauge control and rollbending devices produce strip having satisfactory shape following cold reduction.

EXAMPLE 4 A -ton heat of steel was melted in an electric furnace and killed by vacuum deoxidation. The steel had the following analysis:

Wt. Carbon 0.005 Manganese 0.37 Phosphorus 0.01 l Sulphur 0.017 Nitrogen 0.007 Silicon 0.01

Balance iron A 600 pound ingot from this heat was hot rolled in the laboratory into strip 0.06 inch thick. After pickling, the hot-rolled strip was cold reduced by 82 percent to a final gauge of 0.011 inch. Samples of the strip were tested and found to have a longitudinal yield strength of 112,250 psi. and a transverse dynamic elongation of 1.5 percent. Can ends were satisfactorily fabricated therefrom.

In view of the results of Example 4, it appears that the minimum transverse dynamic elongation required for consistently satisfactory fabrication of can ends may be considerably less for the steels of the invention than for steels made in accordance with the prior art.

In each of the above examples, the nonmetallic inclusions in the steels were of the same general type as those shown in FIG. 2.

1f the carbon and/or manganese contents approach the lower ends of our ranges, the percentage of cold reduction should approach the upper limit of our range in order to obtain the required yield strength. lf these elements approach the upper ends of our ranges, the percentage of cold reduction should be correspondingly less.

While we have described the invention in connection with coated products, the steels are useful in the uncoated condition for applications having requirements similar to those of can end stock.

We claim:

1. A full-hard killed steel sheet having a metallic coating thereon, said sheet having a maximum thickness of 0.0140 inch, a minimum yield strength of 100,000 psi. and sufficient formability to be formed into can ends and double seamed onto can bodies, said steel consisting essentially of 0.10 wt. max. carbon, 0.15 to 0.60 wt. manganese, 0.040 wt. percent max. sulfur, 0.008 wt. percent max. nitrogen, balance iron, the weight ratio of the manganese to the sulfur being at least 8:1, the manganese being equal to or less than 0.40 wt. percent when the carbon is equal to or less than 0.08 wt. percent and the sulfur is greater than 0.020 wt. percent, said steel containing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferrite matrix.

2. An article as recited in claim 1, in which said steel has been killed by vacuum deoxidation.

3;. An article as recited in claim 1, said steel containing at least one element from the group consisting of aluminum, zirconium, vanadium, boron and titanium in an amount effective to kill said steel.

4. A full-hard steel sheet having a metallic coating thereon, said sheet having a maximum thickness of 0.0140 inch and containing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferriate matrix, said steel sheet having a minimum yield strength of 100,000 psi. and sufficient formability to be formed into can ends and double seamed onto can bodies, said steel consisting essentially of 0.08 wt. percent max. carbon, 0.15 to 0.60 wt. percent manganese, 0.040 wt. percent max. sulfur, 0.008 wt. percent max. nitrogen, at least one element from the group consisting of aluminum, zirconium, vanadium, boron and titanium in an amount effective to kill said steel, balance iron, the weight ratio of the manganese to the sulfur being at least 8:1, the manganese being equal to or less than 0.40 wt. percent when the sulfur is greater than 0.020 wt. percent.

5. A full-hard killed steel sheet having a metallic coating thereon, said sheet having a maximum thickness of 0.0115 inch and containing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferrite matrix, said steel sheet having a minimum yield stength of 100,000 psi. and sufficient formability to formed into can ends and double seamed onto can bodies, said steel consisting essentially of 0.04 to 0.08 wt. percent carbon, 0.25 to 0.40 wt. percent manganese, 0.030 wt. percent max. sulfur, 0.008 wt. percent max. nitrogen, 0.02 to 0.10

wt. percent aluminum, balance iron, the weight ratio of the manganese to the sulfur being at least 8:1.

6. A can end formed of the steel sheet of claim 1.

7. A method of producing a fullhard steel strip having a metallic coating thereon, said steel strip having a minimum yield strength of 100,000 psi. and sufficient formability to be formed into can ends and double seamed onto can bodies, comprising:

a. hot rolling into intermediate gauge strip a killed steel consisting essentially of 0.10 wt. percent maximum carbon, 0.15 to 0.60 wt. percent manganese, 0.040 wt. percent maximum sulfur, 0.008 wt. percent max. nitrogen, balance iron, the weight ratio of the manganese to the sulfur being at least 8zl, the manganese being equal to or less than 0.40 wt. percent when the carbon is equal to or less than 0.08 wt. percent and the sulfur is greater than 0.020 wt. percent, said steel containing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferrite matrix,

b. cold reducing said steel strip by 65 to 95 percent to a final gauge of 0.0140 inch max. without annealing said steel during said cold reducing, and

c. applying a metallic coating to said strip in its fullhard condition.

8. A method as recited in claim 10, in which the steel is killed by vacuum deoxidation.

9. A method as recited in claim 7 in which the steel is killed by the addition of at least one element from the group consisting of aluminum, zirconium, vanadium, boron and titanium.

10. A method of producing a full-hard steel strip, having a metallic coating thereon, said steel having a minimum yield strength of 100,000 psi. sufficient formability to be formed into can ends and double seamed onto can bodies, comprising:

a. hot rolling into intermediate gauge strip a steel consisting essentially of 0.08 wt. percent max. carbon, 0.15 to 0.60 wt. percent manbanese, 0.040 wt. percent max. sulfur, 0.008 wt. percent max. nitrogen, at least one element from the group consisting of aluminum, zirconium, vanadium, boron and titanium in an amount effective to kill said steel, balance iron, the weight ratio of the manganese to the sulfur being at least 8:2, the manganese being equal to or less than 0.040 wt. percent when the sulfur is greater than 0.020 wt. percent, said steel contain' ing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferrite matrix,

b. cold reducing said steel strip by 65 to percent of a final gauge of 0.0140 inch max., without annealing said steel during said cold reducing, and

c. applying a metallic coating to said strip in its fullhard condition.

1 l. A method of producing a full-hard steel strip having a metallic coating thereon, said steel having a minimum yield strength of 100,000 psi. and sufficient formability to be formed into can ends and double seamed onto can bodies, comprising:

a. hot rolling into intermediate gauge strip a steel of the composition recited in claim 5,

b. cold reducing said steel strip by 65 to 95 percent to a final gauge of 0.0115 inch max., without annealing said steel during said cold reducing, and

c. applying a metallic coating to said strip in its fullhard condition. 

2. An article as recited in claiM 1, in which said steel has been killed by vacuum deoxidation.
 3. An article as recited in claim 1, said steel containing at least one element from the group consisting of aluminum, zirconium, vanadium, boron and titanium in an amount effective to kill said steel.
 4. A full-hard steel sheet having a metallic coating thereon, said sheet having a maximum thickness of 0.0140 inch and containing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferriate matrix, said steel sheet having a minimum yield strength of 100, 000 psi. and sufficient formability to be formed into can ends and double seamed onto can bodies, said steel consisting essentially of 0.08 wt. percent max. carbon, 0.15 to 0.60 wt. percent manganese, 0.040 wt. percent max. sulfur, 0.008 wt. percent max. nitrogen, at least one element from the group consisting of aluminum, zirconium, vanadium, boron and titanium in an amount effective to kill said steel, balance iron, the weight ratio of the manganese to the sulfur being at least 8:1, the manganese being equal to or less than 0.40 wt. percent when the sulfur is greater than 0.020 wt. percent.
 5. A full-hard killed steel sheet having a metallic coating thereon, said sheet having a maximum thickness of 0.0115 inch and containing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferrite matrix, said steel sheet having a minimum yield stength of 100, 000 psi. and sufficient formability to formed into can ends and double seamed onto can bodies, said steel consisting essentially of 0.04 to 0.08 wt. percent carbon, 0.25 to 0.40 wt. percent manganese, 0.030 wt. percent max. sulfur, 0.008 wt. percent max. nitrogen, 0.02 to 0.10 wt. percent aluminum, balance iron, the weight ratio of the manganese to the sulfur being at least 8:1.
 6. A can end formed of the steel sheet of claim
 1. 7. A method of producing a full-hard steel strip having a metallic coating thereon, said steel strip having a minimum yield strength of 100,000 psi. and sufficient formability to be formed into can ends and double seamed onto can bodies, comprising: a. hot rolling into intermediate gauge strip a killed steel consisting essentially of 0.10 wt. percent maximum carbon, 0.15 to 0.60 wt. percent manganese, 0.040 wt. percent maximum sulfur, 0.008 wt. percent max. nitrogen, balance iron, the weight ratio of the manganese to the sulfur being at least 8:1, the manganese being equal to or less than 0.40 wt. percent when the carbon is equal to or less than 0.08 wt. percent and the sulfur is greater than 0.020 wt. percent, said steel containing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferrite matrix, b. cold reducing said steel strip by 65 to 95 percent to a final gauge of 0.0140 inch max. without annealing said steel during said cold reducing, and c. applying a metallic coating to said strip in its full-hard condition.
 8. A method as recited in claim 10, in which the steel is killed by vacuum deoxidation.
 9. A method as recited in claim 7 in which the steel is killed by the addition of at least one element from the group consisting of aluminum, zirconium, vanadium, boron and titanium.
 10. A method of producing a full-hard steel strip, having a metallic coating thereon, said steel having a minimum yield strength of 100,000 psi. sufficient formability to be formed into can ends and double seamed onto can bodies, comprising: a. hot rolling into intermediate gauge strip a steel consisting essentially of 0.08 wt. percent max. carbon, 0.15 to 0.60 wt. percent manbanese, 0.040 wt. percent max. sulfur, 0.008 wt. percent max. nitrogen, at least one element from the grOup consisting of aluminum, zirconium, vanadium, boron and titanium in an amount effective to kill said steel, balance iron, the weight ratio of the manganese to the sulfur being at least 8:2, the manganese being equal to or less than 0.040 wt. percent when the sulfur is greater than 0.020 wt. percent, said steel containing nonmetallic inclusions predominantly in the form of small discrete particles well dispersed throughout the ferrite matrix, b. cold reducing said steel strip by 65 to 95 percent of a final gauge of 0.0140 inch max., without annealing said steel during said cold reducing, and c. applying a metallic coating to said strip in its full-hard condition.
 11. A method of producing a full-hard steel strip having a metallic coating thereon, said steel having a minimum yield strength of 100,000 psi. and sufficient formability to be formed into can ends and double seamed onto can bodies, comprising: a. hot rolling into intermediate gauge strip a steel of the composition recited in claim 5, b. cold reducing said steel strip by 65 to 95 percent to a final gauge of 0.0115 inch max., without annealing said steel during said cold reducing, and c. applying a metallic coating to said strip in its full-hard condition. 